Synthesis of fused tetrazolone derivatives

Article abstract of DOI:10.3906/kim-1303-90

New fused tetrazolone derivatives were synthesized using homophthalic and maleic anhydrides. Treatment of anhydrides with trimethylsilyl azide opened the lactone rings and formed the corresponding intermediates, which bore 1,3-dipole and dipolarophile functionalities in ortho positions. The intermediates partially underwent internal 1,3-dipolar cycloaddition to produce fused tetrazolone derivatives. When the carbonyl groups in anhydride were not conjugated with any double bond, then a triazine-fused tetrazolone derivative was formed. TUeBITAK.

Full text of DOI:10.3906/kim-1303-90

Turk J Chem
Turkish Journal of Chemistry
(2013) 37: 610 – 618
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http://journals.tubitak.gov.tr/chem/
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c
⃝ TUBITAK
doi:10.3906/kim-1303-90
Research Article
Synthesis of fused tetrazolone derivatives
1
Sevil OZCAN, Zeynep EKMEKC¸ I,
1,2
1
Berk MUJDE, Metin BALCI1,∗
¨
˙
¨
1Department of Chemistry, Middle East Technical University, Ankara, Turkey
2Department of Chemistry, Su¨leyman Demirel University, Isparta, Turkey
Received: 27.03.2013
•
Accepted: 10.05.2013
•
Published Online: 12.07.2013
•
Printed: 05.08.2013
Abstract: New fused tetrazolone derivatives were synthesized using homophthalic and maleic anhydrides. Treatment of
anhydrides with trimethylsilyl azide opened the lactone rings and formed the corresponding intermediates, which bore
1,3-dipole and dipolarophile functionalities in ortho positions. The intermediates partially underwent internal 1,3-dipolar
cycloaddition to produce fused tetrazolone derivatives. When the carbonyl groups in anhydride were not conjugated with
any double bond, then a triazine-fused tetrazolone derivative was formed.
Key words: Tetrazolone, acyl azide, Curtius rearrangement, 1,3-dipole, dipolarophile, 1,3-dipolar cycloaddition
1. Introduction
Heterocyclic compounds display a broad spectrum of biological activities. Among the nitrogen-containing
heterocycles, tetrazolones1 have attracted considerable attention due to their excellent herbicidal activity.2,3
One of the best known tetrazolone derivatives as a commercial herbicide is fentrazamide (1), which is highly
effective against many weeds and inhibits cell division.4 Another important example of tetrazolones is 1-aryl-4-
(3-fluoropropyl)-tetrazolone (2), which was developed as a new and highly active family of protoporphyrinogen
oxidase-inhibiting herbicides.5
The tetrazolone scaffold is especially important for pesticide development and the most general synthetic
approach for tetrazolone synthesis involves 1,3-dipolar cycloaddition reaction of azides to isocyanates (Scheme
1).
∗Correspondence: mbalci@metu.edu.tr
In memory of Prof Dr Ayhan S. Demir
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Scheme 1. The synthesis of 1,4-disubstituted tetrazolone.
The reaction of aryl isocyanates with either sodium azide or aluminum azide to form tetrazolones has
long been known in the literature.6−8 Trimethylsilyl azide (TMSA), in analogy with azides, also behaves as a
1,3-dipole towards isocyanates to synthesize tetrazolones.9,10 For example, 1.3-dipolar cycloaddition of phenyl
isocyanate to excess of TMSA has been reported to afford the corresponding tetrazolone derivative.10 As an
alternative to TMSA, Salama et al. have recently reported an inexpensive, in situ generated SiCl4 /NaN3
combination that can be used as 1,3-dipole towards isocyanates to produce tetrazolones.11 In the literature,
there is a continuous focus on 1- and 4-substituted tetrazolone derivatives, which have been proved to show
important herbicidal activities.2−5 To the best of our knowledge, the synthesis or herbicidal activity of fused
tetrazolones has not been reported yet. Herein, we report a simple, mild, and one-pot synthesis of novel fused
tetrazolone derivatives starting from anhydrides.
2. Results and discussion
Our primary goal was the synthesis of 6, which is an important precursor to undergo further cyclization reactions
to produce heterocyclic compounds. As the starting material, homophthalic acid and its derivatives were used.
Scheme 2. Synthesis of fused tetrazolone derivatives 7 starting from the substituted homophthalic acids 4.
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Bromo and methoxy homophthalic acids 4b and 4c were synthesized using the protocols reported in one of our
recent studies.12 For the synthesis of 5, the acids were treated with thionyl chloride in dichloromethane and
the corresponding anhydrides 513 were obtained in high yields. The anhydride 5a–c were reacted with TMSA
and thionyl chloride, followed by a second molar equivalent of TMSA and methanol, respectively, as shown
in Scheme 2. Analysis of the products indicated the formation of tetrazolones (7a–b) in 36%–38% yields and
isoindolinones (8a–c) in 32%–53% yields instead of the expected product 6. This result was not that surprising
since the intermediates formed during this reaction have the potential to form isocyanate as dipolarophile and
acyl azide as 1,3-dipole to undergo a 1,3-dipolar cycloaddition reaction.
The suggested mechanism for the formation of 7a–b and 8a–c is shown in Scheme 3. Under the reaction
conditions, the lactones 5 first undergo ring opening reaction with TMSA to form intermediates 9a–c. Under
the refluxing conditions, Curtius rearrangement takes place and forms the intermediates 10a–c. Subsequent
addition of thionyl chloride followed by second molar equivalent of TMSA converts trimethylsilyl esters 10
into acyl azide intermediates 11, which bear 1,3-dipole and dipolarophile functionalities in ortho positions.
The intermediates 11a–b partially undergo internal 1,3-dipolar cycloaddition to produce fused tetrazolone
derivatives 7a–b. Moreover, isocyanate is partially trapped with methanol to form the intermediates 12a–c.
The attack of lone pairs on urethane NH on the azide carbonyl results in the formation of isoindolinones 8a–c.
Methoxy substituted anhydride 5c only produces isoindolinone derivative 8c, favoring the intermediate 12c.
Scheme 3. Suggested mechanism for the formation of 7a–b and 8a–c.
In order to test the effect of the benzene ring on the mode of this reaction, we first synthesized the
anhydride 1314 by the addition of maleic anhydride to in situ generated butadiene. The anhydride 13 was
treated with TMSA under the same reactions conditions as described above. However, the reaction produced
15 instead of the expected product 14.
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Scheme 4. Synthesis of a 1,2,4-trazinan-3-one fused tetrazolone derivative 15.
The tetrazolone derivative 15 was characterized by spectral methods. The number of nitrogen atoms
was determined by elemental analysis. According to the results of HRMS and elemental analysis, compound 15
contains 5 nitrogen atoms. The NH proton was observed at 7.62 ppm as a singlet. The 13 C NMR revealed the
presence of 2 carbonyl carbon atoms resonating at 153.9 and 153.5 ppm, indicating the connection to 2 nitrogen
atoms from both sides of the carbonyl groups. In the HMBC spectrum (Figure 1), carbonyl carbon resonances
correlate with the proton resonances appearing at 4.37 (H10a) and 3.97 (H7a) as well as with the NH proton
resonating at 7.62 ppm. These correlations support the exact positions of the carbonyl groups.
Figure. HMBC spectrum of compound 15.
The following mechanism was suggested for the formation of the product 15 (Scheme 5). The anhydride
13 first undergoes a ring opening reaction with TMSA to form the intermediate 16. Then the acyl azide
functionality in 16 rearranges to the isocyanate 17. Reaction of 17 with thionyl chloride followed by a second
molar equivalent of TMSA converts trimethylsilyl ester into acyl azide 18, which prefers the rearrangement
to the corresponding bisisocyanate 19 instead of intramolecular addition to the isocyanate group to give 14.
Bisisocyanate 19 reacts with TMSA to form the intermediate 20, which then undergoes an internal addition
reaction to produce fused tetrazolone derivatives 15.
Our experimental results allow us to conclude that under the same reaction conditions anhydrides 5 and
13 show different reactivity. In the case of 5, there are 2 different acyl azide functionalities, with one of the
carbonyl groups conjugated with the benzene ring and the other one not. Recently, we showed that the stability
of those acyl azides is different and the conjugated one is more stable than the other.15 However, in the case
of 13, neither of the acyl azide functions is in conjugation with any other groups so that neither of them will
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be as stable as the conjugated one and they will be expected to undergo Curtius rearrangement much faster.
However, one of the acyl azide groups generated from 5 is stabilized due to the conjugation with the benzene
ring and therefore prefers addition to the isocyanate group over rearrangement. As a result of this reactivity
difference, the formed products starting from 5 and 13 are different.
Scheme 5. Suggested mechanism for the formation of 15.
In conclusion, we developed a new practical and efficient route to novel fused tetrazolone as well as
to isoindolinone derivatives starting from cheap and readily available reagents such as homophthalic acid
derivatives and maleic anhydride. The mild reaction conditions, easy work-up procedure, and simple operation
are advantages of this procedure.
3. Experimental section
3.1. General
Melting points were determined on a Thomas-Hoover capillary melting point apparatus. IR spectra were
recorded on a PerkinElmer 980 spectrometer. NMR spectra were recorded on a Bruker-Avance instrument at
400 MHz for 1 H and 100 MHz for 13 C NMR. Apparent splitting is given in all cases. Column chromatography
was performed on silica gel (60-mesh, Merck). TLC was carried out on Merck 0.2 mm silica gel 60 F254 analytical
aluminum plates. Elemental analyses were carried out on a Leco-932 model CHNS analyzer.
3.2. Isochroman-1,3-dione (5a)
To a stirred solution of homophthalic acid (5.0 g, 27.8 mmol) in dichloromethane (100 mL) was added an excess
amount of thionyl chloride (5 mL, 68 mmol). The reaction mixture was refluxed until a clear solution was
formed (3 h). After the completion of the reaction, the solvent and excess thionyl chloride were evaporated
under reduced pressure to obtain 5a (4.4 g, 97%) as a yellow solid, mp 143–144 ◦ C (Lit. 144–145 ◦ C16). 1 H
NMR (400 MHz, CDCl3)δ 8.22 (br d, J9,10 = 7.8 Hz, 1H, H-10), 7.70 (br dd, J9,10 = 7.8 Hz, J8,9 = 7.6
Hz, 1H, H-9), 7.52 (br t, J8,9 = J7,8 = 7.6 Hz, 1H, H-8), 7.35 (br d, J7,8 = 7.6 Hz, 1H, H-7), 4.14 (s, 2H,
H-3); 13 C NMR (100 MHz, CDCl3)δ 165.0, 161.3, 135.9, 134.7, 131.3, 129.1, 127.9, 121.9, 34.7; Anal. Calcd
for C9 H6 O3 : C, 66.67; H, 3.73. Found: C, 66.48; H, 4.06.
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3.3. 7-Bromoisochroman-1,3-dione (5b)17,18
The same procedure for 5a was followed except using 5-bromo-2-(carboxymethyl)benzoic acid (4b) (5.0 g, 19
mmol) and thionyl chloride (5 mL, 68 mmol). The product 5b (4.5 g, 18.6 mmol, 98%) was obtained as a pale
yellow solid, mp 171–173 ◦ C. 1 H NMR (400 MHz, CDCl3)δ 8.26 (br s, 1H, H-10), 7.73 (br dd, J8,7 = 8.2
Hz, J8,10 = 1.6 Hz, 1H, H-8), 7.16 (br d, J7,8 = 8.2 Hz, 1H, H-7), 4.02 (s, 2H, H-3); 13 C NMR (100 MHz,
CDCl3)δ 161.2, 157.2, 136.0, 131.1, 130.5, 126.6, 120.9, 120.1, 31.6; IR (KBr, cm−1) 3094, 2949, 1796, 1780,
1296, 1195, 1177, 1060, 906, 762, 727; Anal. Calcd. for C9 H5 BrO3 ; C, 44.85; H, 2.09; Br, 33.15 Found: C,
44.69; H, 2.20.
3.4. 7-Methoxyisochroman-1,3-dione (5c)18
The same procedure for 5a was followed except using 2-(carboxymethyl)-5-methoxybenzoic acid (5.0 g, 23.7
mmol) and thionyl chloride (5 mL, 68 mmol). The product 5c (4.4 g, 96%) was obtained as a pale yellow solid,
mp 180–182 ◦ C. 1 H NMR (400 MHz, CDCl3)δ 7.58 (d, J10,8 = 2.0 Hz, 1H, H-10), 7.19–7.17 (m, 2H, H-8 and
H-7), 4.01 (s, 2H, H-3), 3.82 (s, 3H, -OCH3); 13 C NMR (100 MHz, CDCl3)δ 164.9, 161.2, 159.9, 128.8, 126.6,
124.2, 122.7, 113.2, 56.0, 34.0.
3.5. Synthesis of 3H -tetrazolo[2,1-b]phthalazine-3,10(5H )-dione (7a) and methyl 1-oxoisoindoline-
2-carboxylate (8a)
To a stirred solution of homophthalic anhydride (5a) (1.05 g, 6.5 mmol) in THF (25 mL) was added 1.2
equivalent of trimethylsilyl azide (TMSA) (1.02 mL, 7.8 mmol), followed by refluxing for 3 h. THF was
evaporated and the residue was dissolved in CCl4 (25 mL) and to this mixture was added thionyl chloride (0.53
mL, 7.8 mmol). The resulting mixture was refluxed for 3 h and the solvent was evaporated and the remaining
residue was dissolved in THF (25 mL) and to this mixture was added a second molar equivalent of TMSA (1.02
mL, 7.8 mmol). After 3 h of refluxing the solvent was removed and the residue was dissolved in methanol (25
mL) and further refluxed for 3 h. Methanol was evaporated and the residue was chromatographed on silica gel
(40 g) eluting with EtOAc/hexane (3/2) to give the compounds 7a (0.5 g, 38%) and 8a (0.5 g, 40%). The
obtained products were further purified by recrystallization from EtOAc/hexane (5:1). 3H -Tetrazolo[2,1-
b]phthalazine-3,10(5H )-dione (7a). Pale yellow solid, mp 281–283 ◦ C. 1 H NMR (400 MHz, CDCl3)δ 7.86
(d, J10,11 = 7.5 Hz, 1H, H-10), 7.63 (t, J10,11 = J11,12 = 7.5 Hz, 1H, H-11), 7.46 (m, 2H, H-12, H-13), 4.39 (s,
2H, H-9); 13 C NMR (100 MHz, CDCl3)δ 165.6, 154.4, 140.7, 134.3, 130.4, 128.9, 125.5, 123.3, 49.2; IR (KBr,
cm−1) 2251, 1744, 1695, 1363, 1337, 1282, 1213, 1194, 1158, 722, 554; Anal. Calcd. for C9 H6 N4 O2 : C, 53.47;
H, 2.99; N, 27.71 Found: C, 53.21; H, 3.38; N, 27.49.
Methyl 1-oxoisoindoline-2-carboxylate (8a).19 White solid, mp 143–147 ◦ C. 1 H NMR (400 MHz,
CDCl3)δ 7.78 (d, J8,9 = 7.5 Hz, 1H, H-9), 7.57 (t, J7,8 = J8,9 = 7.5 Hz, 1H, H-8), 7.46 (d, J6,7 = 7.5 Hz,
1H, H-6) 7.42 (t, J6,7 = J7,8 = 7.5 Hz, 1H, H-7), 4.72 (s, 2H, H-2), 3.85 (s, 3H, -OCH3); 13 C NMR (100 MHz,
CDCl3)δ 171.4, 157.4, 146.4, 138.9, 136.1, 133.7, 129.9, 128.5, 58.5, 54.3; IR (KBr, cm−1) 2956, 2251, 1785,
1598, 1469, 1263, 1190, 1103, 1019, 999, 884, 771, 681, 581, 479; Anal. Calcd. for C10 H9 NO3 : C, 62.82; H,
4.74; N, 7.33 Found: C, 62.51; H, 4.48; N, 7.70.
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3.6. Synthesis of 7-bromo-3H -tetrazolo[2,1-b]phthalazine-3,10(5H )-dione (7b) and methyl 6-bromo-
1-oxoisoindoline-2-carboxylate (8b)
The same procedure for 7a and 8a was followed except using 7-bromoisochroman-1,3-dione (5b) (1.56 g, 6.5
mmol), TMSA (1.02 mL, 7.8 mmol), thionyl chloride (1.6 mL, 23.4 mmol), and TMSA (1.02 mL, 7.8 mmol).
The products were chromatographed on silica gel (40 g) eluting with EtOAc/hexane (3/2) to give compounds
7b (0.65 g, 36%) and 8b (0.56 g, 32%).
7-Bromo-3H -tetrazolo[2,1-b]phthalazine-3,10(5H)-dione (7b). 1 H NMR (400 MHz, CDCl3)δ
8.0 (d, J10,12 = 2.0 Hz, 1H, H-10), 7.73 (dd, J12,10 = 2.0 Hz, J12,13 = 6.2 Hz, 1H, H-12), 7.33 (d, J13,12 = 6.2
Hz, 1H, H-13), 4.74 (s, 2H, H-9a,b); 13 C NMR (100 MHz, CDCl3)δ: 164.5, 154.7, 139.5, 137.7, 132.7, 128.8,
135.3, 132.2, 49.3; IR (KBr, cm−1) 2957, 2260, 2160, 1799, 1758, 1757, 1325, 1251, 1145, 1057, 1026, 913, 842,
736.
Methyl 6-bromo-1-oxoisoindoline-2-carboxylate (8b).19b Pale yellow solid, mp 186–188 ◦ C. 1 H
NMR (400 MHz, CDCl3)δ: 8.1 (d, J7,9 = 2.0 Hz, 1H, H-9), 7.77 (dd, J7,9 = 2.0 Hz, J6,7 = 6.2 Hz, 1H, H-7),
7.38 (d, J6,7 = 6.2 Hz, 1H, H-6), 4.80 (s, 2H, H-2a,b), 3.99 (s, 3H, -OCH3); 13 C NMR (100 MHz, CDCl3)δ:
165.0, 153.6, 139.6, 137.1, 133.3, 128.6, 125.1, 123.6, 54.2, 49.2; IR (KBr, cm−1) 3058, 3007, 2949, 2848, 1767,
1695, 1438, 1363, 1320, 1256, 1208, 1139, 1005, 886, 848.
3.7. Synthesis of methyl 6-methoxy-1-oxoisoindoline-2-carboxylate (8c)
The same procedure for 7a and 8a was followed except using 7-methoxyisochroman-1,3-dione (5c) (1.25 g, 6.5
mmol), TMSA (1.02 mL, 7.8 mmol), thionyl chloride (0.53 mL, 7.8 mmol), and TMSA (1.02 mL, 7.8 mmol).
The residue was chromatographed on silica gel (40 g) eluting with EtOAc/hexane (3/2) to obtain compound
8c (0.76 g, 53%) as a single product.
Methyl 6-methoxy-1-oxoisoindoline-2-carboxylate (7c).19b 1 H NMR (400 MHz, CDCl3)δ 7.63 (d,
J7,9 = 2.8 Hz, 1H, H-9), 7.19 (d, J6,7 = 8.4 Hz, 1H, H-6), 7.07 (dd, J6,7 = 8.4 Hz, J7,9 = 2.8 Hz, 1H, H-7),
3.99 (s, 2H, H-2a,b), 3.86 (s, 3H, -OCH3), 3.70 (s, 3H, -OCH3); 13 C NMR (100 MHz, CDCl3)δ: 164.8, 158.7,
139.4, 133.5, 128.8, 125.1, 119.7 116.5, 55.5, 51.9, 39.8.
3.8. Synthesis of 6a,7,10,10a-tetrahydro-1H -tetraazolo[1,2-a][1,2,4]benzotri-azine-1,5(6H )-dione
(15)
To a stirred solution of 1,2,3,6-tetrahydrophthalic anhydride (13) (1.0 g, 6.6 mmol) in THF (40 mL) was added
TMSA (1.06 g, 9.2 mmol) and the solution was heated to reflux temperature. N2 evolution was over after 30–45
min. The solution was cooled and concentrated in vacuum. The residue was dissolved in CCl4 (20 mL) and
to this solution was added DMF (3 drops) followed by SOCl2 (0.347 g, 2.92 mmol). The reaction mixture was
heated to 40–50 ◦ C. The reaction was monitored by IR. When the infrared absorption at 1720 cm−1 (ester)
disappeared (30–45 min), the solution was cooled to room temperature and concentrated in vacuum (bath
temperature should be below 35 ◦ C). The remaining residue was dissolved in THF (25 mL) and to this solution
was added TMSA (1.06 g, 9.02 mmol) at r.t., which was subsequently heated to 80–85 ◦ C for 90 min. After
the reaction was completed, the solution was cooled to room temperature. Brown precipitate was filtered and
washed with CH2 Cl2 and the residue was crystallized from hot ethanol to give product 15 (1.15 g, 61%) as
colorless crystals, mp 143–144 ◦ C. 1 H NMR (400 MHz, DMSO-d6)δ 7.62 ppm (s, 1H, -NH-), 5.85–5.80 (m,
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2H, H8 and H9), 4.37 (q, J = 4.6 Hz, 1H, H10a), 3.97 (q, J = 4.1 Hz, 1H, H7a), 2.36 (dd, J = 15.6 and J =
4.4 Hz, 1H), 2.24 (m, 1H), 2.20–2.06 (m, 2H); 13 C NMR (100 MHz, DMSO, ppm) δ 153.9, 153.5, 127.6, 127.3,
54.2, 46.9, 28.1, 26.5; IR (KBr, cm−1) 3344, 3316, 3043, 2970, 2171, 2152, 1751,176, 1340, 1179, 627; Anal.
Calcd. for C8 H9 N5 O2 : C, 46.38; H, 4.38; N, 33.80 Found: C, 46.41; H, 4.36; N: 34,19; HRMS: Anal. Calcd.
for C8 H9 N5 O2 [M+H]+ : 208.0829. Found [M+H]+ : 208.0879.
Acknowledgments
¨
The authors are indebted to the Scientific and Technological Research Council of Turkey (TUBITAK, Grant
˙
Nos 108-M-168 and TBAG-110 R 001), the Department of Chemistry at Middle East Technical University, and
¨
the Turkish Academy of Sciences (TUBA) for their financial support of this work.
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